The objective of this proposal is to define strain- and opacity-related surface antigens in Neisseria gonorrhoeae which determine pathogenicity and mediate interactions with host defense systems. Opaque and transparent colonial variants of strains from patients with disseminated gonococcal infection (DGI) and from patients with local genital infection will be tested for (1) their sensitivity to the bactericidal action of normal human serum (NHS), (2) their ability to stimulate oxidative metabolism by attachment to human polymorphonuclear leukocytes (PMN), and (3) their capacity to be opsonized for phagocytosis by specific immune antisera. To further define the mechanism of serum resistance, NHS will be absorbed with serum-resistant and serum-sensitive strains, and with isolated outer membrane components coupled to affinity columns. Also, the bactericidal or inhibitory activity of antibodies specific for purified surface antigens will be determined. Such monospecific antibodies will also be used to define surface structures which mediate attachment to PMN and/or stimulation of PMN, and which serve as binding sites for opsonic antibodies. These studies should suggest which surface antigens on the gonococcus have potential as candidates for vaccine development.